1. Field of the Invention
The present invention relates to a melt-kneading method for resin performed in a condition where a filling material is dispersed in a resin as well as a melt-kneaded resin product obtained by such melt-kneading method for resin; a molding method connected to such melt-kneading method for resin as well as a molded product obtained by such molding method; a molded resin product constituted by such molded product; and a substance permeating membrane or separation membrane constituted by such molded resin product as well as a gradual substance release material or support material for cell culturing constituted by such molded resin product.
2. Description of the Related Art
It has been a well-known fact that in a higher-order structure produced by blending a pair of incompatible polymers, one polymer becomes a matrix while the other polymer becomes a dispersion phase to form a sea-island structure.
This sea-island structure undergoes a phase conversion under conditions where the composition of the polymers constituting the blend becomes roughly proportional to the ratio of melt viscosities of the respective polymers, and as the blend composition and viscosity ratio change from the levels under the aforementioned conditions, the relationship of sea and island reverses. The higher-order structure that appears in a state near the conditions under which a phase conversion occurs is so-called a “co-continuous structure” where two types of polymers form mutually continuous phases. Accordingly, in any blend comprising incompatible polymers, a co-continuous structure always appears according to the aforementioned blend composition and ratio of viscosities of constituent polymers (S. Steinmann, W. Gronski, C. Friedrich, Polymer, 2002, 43, 4467 (Non-patent Literature 1); F. Gubbels, S. Blacher, E. Vanlathem, R. Jerome, R. Deltour, F. Brouers, Ph. Teyssie, Macromolecules, 1995, 28, 1559 (Non-patent Literature 2)).
Unlike the sea-island structure, this co-continuous structure forms mutually continuous phases and is known to express various physical properties that reflect such structure, with a wide range of ideas proposed for applying these physical properties. For example, use of a conductive polymer for one continuous phase allows for development of a material that takes advantage of the beneficial features of electrical conductivity or anti-electricity (Patent Literature 1). By removing one phase from the co-continuous structure using a solvent, etc., a mesoporous material comprising the other phase can be formed with ease, and methods to apply such mesoporous material as a separation membrane or filter according to the size of the material are proposed (Patent Literature 2, Patent Literature 3, Patent Literature 4). Technologies are also available to use a supercritical fluid process or other means to foam one phase in a material comprising an incompatible polymer blend. However, these technologies based on foaming only form pores of approx. several tens of micrometers in size near the surface of a bulk material, and such bulk material cannot be used to selectively cause a given substance to permeate through.
As for utilization of this co-continuous structure, traditionally a melt-kneaded product is obtained using an extruding machine, etc., and then the obtained product is molded into various shapes and used, as mentioned above. In addition to the above, there are also applications whereby a co-continuous structure is manufactured from an incompatible polymer blend, after which one of the incompatible polymers is removed using a solvent to obtain a porous material and this porous material is utilized.
For example, Japanese Patent Laid-open No. 2006-136673 (Patent Literature 6) achieves a block-type support material for use in cell engineering comprising a bio-absorbent polymer material that has a three-dimensional netlike structure having small pores of 5 to 50 μm in size and where irregular continuous pores account for 20 to 80% of the cross-section area of the structure; wherein such bio-absorbent polymer material is selected from polyglycolic acid, polylactic acid and lactic acid-glycolic acid copolymer, among others. The shape of such material is characterized by a particle size of 300 to 700 μm and average pore size of 5 μm, and specifically a small-pore structure having irregular continuous pores of 5 to 50 μm in size is described (Example 1). Similarly in Japanese Patent Laid-open No. 2006-306983 (Patent Literature 7), a porous material having continuous pores of 1 to 30 μm in average pore size is described. From the above, it is shown that the shapes of porous materials, especially shapes of formed porous materials, have high degrees of non-uniformity and that a co-continuous structure comprising an incompatible polymer blend and forming any such shaped porous material is a random structure having little regularity.
Because of the above, the co-continuous structure comprising an incompatible polymer blend as mentioned above is thermally unstable and when such co-continuous structure is thermally processed or annealed at high temperature, for example, a structural relaxation occurs to inevitably enlarge the continuous phase size in the original structure that has been formed. In other words, a polymer blend obtained this way presents a technical problem of poor thermal stability, which makes it essential to find a way to obtain a molded resin product having a stable co-continuous structure. Also, a co-continuous structure is not only thermally unstable, but it is also characterized in that the continuous phase size is determined uniquely by the composition of the blend and ratio of viscosities of constituent polymers. Because of this, controlling the continuous phase size in a desired manner using external parameters is considered difficult.
A co-continuous structure formed by an incompatible polymer blend is determined by the composition, and ratio of melt viscosities of, the polymers constituting the aforementioned blend, and naturally there is a need to develop a method to control the size of such co-continuous structure in a desired manner using some sort of external parameters.
A mesoporous structure obtained by way of a co-continuous structure has two key characteristics. One is that because the porous structure is formed three-dimensionally, such structure is most ideal for selective permeation of substances. The other is that because the remaining polymer constituting the frame of the mesoporous material, which is not removed using a solvent, also has a three-dimensionally connected structure and therefore even after the other polymer has been removed, the structure remains very strong three-dimensionally just like a natural bone structure.
For these reasons, a co-continuous structure formed by an incompatible polymer blend in a manner allowing the size of the co-continuous structure to be controlled in a desired manner using some sort of external parameters, provides an ideal structure that is thermally stable and whose continuous phase size can be determined uniquely. Also, a shaped porous material formed by way of such structure can provide a mesoporous structure having a uniform shape corresponding to the co-continuous structure.
An overview of prior arts is provided to examine the problems inherent in these conventional technologies. As mentioned above, this co-continuous structure formed by an incompatible polymer blend is thermally unstable and if such co-continuous structure is thermally processed or annealed at high temperature, for example, a structural relaxation occurs to inevitably enlarge the continuous phase size in the original structure that has been formed.
Traditionally, a product comprising an incompatible polymer blend has been processed using a kneading-type extruding machine or molding machine. However, the screw rotation speeds of these machines are around 300 rpm at most, and the shear rates achievable at such screw rotation speeds are only around 100 sec−1. At shear rates of this level, the polymer viscosities or filling material dispersion condition cannot be changed sufficiently during kneading, which makes is impossible to mix the incompatible polymer blend at nano-level or nano-disperse a filling material such as a filler in the resin.
The inventors had already found that with a co-continuous structure obtained by an extruding machine, etc., clay would provide the effect of preventing coalescence of phases (Y. J. Li, H. Shimizu, Polymer, 2004, 45, 7381 (Non-patent Literature 3); Y. J. Li, H. Shimizu, Macromol. Rapid Commun., 2005, 26, 710 (Non-patent Literature 4)).
On the other hand, there have been successful attempts to control the size of a co-continuous structure comprising an incompatible polymer blend by operating an extruding machine under various shear force conditions (P. Potschke, D. R. Paul, Macromol. Symp., 2003, 198, 69 (Non-patent Literature 5); M. Jaziri, T. K. Kallel, S. Mbarek, B. Elleuch, Polym. Int., 2005, 54, 1384 (Non-patent Literature 6)). However, these attempts used narrow ranges of shear forces available on conventional extruding machines, and descriptions regarding the control of the size of a co-continuous structure comprising an incompatible polymer blend are limited. To be specific, screw rotation speeds are around 300 rpm at most, and the shear rates achievable at such screw rotation speeds are only around 100 sec−, as mentioned above. At shear rates of this level, a filling material such as a filler cannot be dispersed sufficiently to the required uniformity at nanometer-level, if the related incompatible polymer matrix is subject to different viscosities. As a result, the above methods do not provide a fundamental solution.
The inventors therefore invented a micro-volume high-shear processing machine equipped with an internal-feedback screw, capable of rotating the screw at a speed of 1000 rpm or more and having a maximum output of 3000 rpm (Japanese Patent Laid-open No. 2005-313608 (Patent Literature 5)).
Using this apparatus, the inventors successfully invented a ferroelectric film being an extruded film product comprising 95 to 20 percent by weight of polyvinylidene fluoride (PVDF) and 5 to 80 percent by weight of polyamide 11 (PA11), wherein such film is produced by rolling an extruded film product of a nano-dispersed polymer blend in which a dispersion phase of polyamide 11 of a size of around 10 nm is dispersed uniformly in a polyvinylidene fluoride matrix phase, and then the rolled film is processed by impressing an alternating electric field (Japanese Patent Laid-open No. 2006-21195 (Patent Literature 8); H. Shimizu, Y. L. Li, A. Kaito, H. Sato, Macromolecules, 2005, 38, 7880 (Non-patent Literature 7); H. Shimizu, Y. L. Li, A. Kaito, H. Sano, J. Nanosci. Nanotechnol., 2006, 6, 12 (Non-patent Literature 8); Y. J. Li, H. Shimizu, T. Furumichi, Y. Takahashi, T. Furukawa, J. Polym. Sci.: Part B: Polym. Phys., 2007, 45, 2707 (Non-patent Literature 9)).
[Patent Literature 1] Japanese Patent Laid-open No. Hei 07-102175 (Japanese Patent No. 3142424)
[Patent Literature 2] U.S. Pat. No. 5,135,627
[Patent Literature 3] Japanese Patent Laid-open No. 2000-1612
[Patent Literature 4] German Patent Laid-open No. 4236935
[Patent Literature 5] Japanese Patent Laid-open No. 2005-313608
[Patent Literature 6] Japanese Patent Laid-open No. 2006-136673
[Patent Literature 7] Japanese Patent Laid-open No. 2006-306983
[Patent Literature 6] Japanese Patent Laid-open No. 2006-21195
[Non-patent Literature 1] S. Steinmann, W. Gronski, C. Friedrich, Polymer, 2002, 43, 4467
[Non-patent Literature 2] F. Gubbels, S. Blacher, E. Vanlathem, R. Jerome, R. Deltour, F. Brouers, Ph. Teyssie, Macromolecules, 1995, 28, 1559
[Non-patent Literature 3] Y. J. Li, H. Shimizu, Polymer, 2004, 45, 7381
[Non-patent Literature 4] Y. J. Li, H. Shimizu, Macromol. Rapid Commun., 2005, 26, 710
[Non-patent Literature 5] P. Potschke, D. R. Paul, Macromol. Symp., 2003, 198, 69
[Non-patent Literature 6] M. Jaziri, T. K. Kallel, S. Mbarek, B. Elleuch, Polym. Int., 2005, 54, 1384
[Non-patent Literature 7] H. Shimizu, Y. L. Li, A. Kaito, H. Sano, Macromolecules, 2005, 38, 7880
[Non-patent Literature 8] H. Shimizu, Y. L. Li, A. Kaito, H. Sano, J. Nanosci. Nanotechnol., 2006, 6, 3923-3928
[Non-patent Literature 9] Y. J. Li, H. Shimizu, T. Furumichi, Y. Takahashi, T. Furukawa, J. Polym. Sci.: Part B: Polym. Phys., 2007, 45, 2707